C++ As A "Better C" Chih-Wei Tang ( 唐之瑋 ) Department of Communication Engineering National Central University JhongLi, Taiwan.

Transcription

1 C++ As A "Better C" Chih-Wei Tang ( 唐之瑋 ) Department of Communication Engineering National Central University JhongLi, Taiwan 2013 Fall

2 Outline 15.2 C A Simple Program: Adding Two Integers 15.5 Header Files 15.6 Inline Functions 15.9 Unary Scope Resolution Operator Function Overloading C.E., NCU, Taiwan 2

3 15.2 C++ C++ Object-oriented Increases software quality and reusability Developed by Bjarne Stroustrup at Bell Labs Called "C with classes" C++ (increment operator) - enhanced version of C Superset of C Can use a C++ compiler to compile C programs Gradually evolve the C programs to C++ ANSI C++ Final version at Free, older version at C.E., NCU, Taiwan 3

4 15.3 A Simple Program: Adding Two Integers (1/3) File extensions C files:.c C++ files:.cpp (which we use),.cxx,.c (uppercase) Differences "comment out" a line : // <iostream> - input/output stream header file all functions must declare their return type C does not require it vcariables in C++ can be defined almost anywhere C.E., NCU, Taiwan 4

5 15.3 A Simple Program: Adding Two Integers (2/3) Input/Output in C++ Performed with streams of characters Streams sent to input/output objects Output std::cout - standard output stream (connected to screen) << stream insertion operator ("put to") std::cout << "hi"; Puts "hi" to std::cout, which prints it on the screen Input std::cin - standard input object (connected to keyboard) >> stream extraction operator ("get from") std::cin >> myvariable; Gets stream from keyboard and puts it into myvariable 5

6 15.3 A Simple Program: Adding Two Integers (3/3) std::endl "end line" Stream manipulator - prints a newline and flushes output buffer Some systems do not display output until "there is enough text to be worthwhile" std::endl forces text to be displayed using statements Allow us to remove the std:: prefix Discussed later Cascading Can have multiple << or >> operators in a single statement std::cout << "Hello " << "there" << std::endl; 6

7 1 // Fig. 15.1: fig15_01.cpp 2 // Addition program 3 #include <iostream> 4 5 int main() 6 { 7 int integer1; 8 9 std::cout << "Enter first integer\n" n"; 10 std::cin >> integer1; int integer2, sum; // declaration std::cout << "Enter second integer\n" n"; 15 std::cin >> integer2; 16 sum = integer1 + integer2; 17 std::cout << "Sum is " << sum << std::endl; return 0; // indicate that program ended successfully 20 } // end function main Enter first integer 45 Enter second integer 72 Sum is 117 7

8 15.6 inline Functions Function calls Cause execution-time overhead Qualifier inline before function return type "advises" a function to be inlined Puts copy of function's code in place of function call Speeds up performance but increases file size Compiler can ignore the inline qualifier inline double cube( const double s ) { return s * s * s; } Using statements By writing using std::cout; we can write cout instead of std::cout in the program Same applies for std::cin and std::endl C.E., NCU, Taiwan 8

9 1 // Fig. 15.3: fig15_03.cpp 2 // Using an inline function to calculate 3 // the volume of a cube. 4 #include <iostream> 5 6 using std::cout; fig15_03.cpp std::cin; std::endl; 7 using std::cin; 8 using std::endl; 9 10 inline double cube( const double s ) { return s * s * s; } int main() 13 { 14 double side; for ( int k = 1; k < 4; k++ ) { 17 cout << "Enter the side length of your cube: "; 18 cin >> side; 19 cout << "Volume of cube with side " 20 << side << " is " << cube( side ) << endl; 21 } // end for return 0; 24 } // end function main 9

10 Enter the side length of your cube: 1.0 Volume of cube with side 1 is 1 Enter the side length of your cube: 2.3 Volume of cube with side 2.3 is Enter the side length of your cube: 5.4 Volume of cube with side 5.4 is

11 1 // Fig. 15.8: fig15_08.cpp 2 // Using default arguments 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 8 int boxvolume( int length = 1, int width = 1, int height = 1 ); 9 10 int main() 11 { 12 cout << "The default box volume is: " << boxvolume() 13 << "\n\nthe nthe volume of a box with length 10,\n" 14 << "width 1 and height 1 is: " << boxvolume( 10 ) 15 << "\n\nthe nthe volume of a box with length 10,\n" 16 << "width 5 and height 1 is: " << boxvolume( 10, 5 ) 17 << "\n\nthe nthe volume of a box with length 10,\n" 18 << "width 5 and height 2 is: " << boxvolume( 10, 5, 2 ) 19 << endl; return 0; 22 } // end function main 23 11

12 24 // Calculate the volume of a box 25 int boxvolume( int length, int width, int height ) 26 { 27 return length * width * height; 28 } // end function boxvolume The default box volume is: 1 The volume of a box with length 10, width 1 and height 1 is: 10 The volume of a box with length 10, width 5 and height 1 is: 50 The volume of a box with length 10, width 5 and height 2 is:

13 15.9Unary Scope Resolution Operator Unary scope resolution operator (::) Access global variables if a local variable has same name Instead of variable use ::variable static_cast<newtype> (variable) Creates a copy of variable of type newtype Convert ints to floats, etc. Stream manipulators Can change how output is formatted setprecision - set precision for floats (default 6 digits) setiosflags - formats output setwidth - set field width C.E., NCU, Taiwan 13

14 1 // Fig. 15.9: fig15_09.cpp 2 // Using the unary scope resolution operator 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 using std::ios; 8 9 #include <iomanip> using std::setprecision; 12 using std::setiosflags; 13 using std::setw; const double PI = ; int main() 18 { 19 const float PI = static_cast< float >( ::PI ); cout << setprecision( 20 ) 22 << " Local float value of PI = " << PI 23 << "\nglobal double value of PI = " << ::PI << endl; 14 24

15 25 cout << setw( 28 ) << "Local float value of PI = " 26 << setiosflags( ios::fixed ios::showpoint ) 27 << setprecision( 10 ) << PI << endl; 28 return 0; 29 } // end function main Borland C++ command-line compiler output Local float value of PI = Global double value of PI = Local float value of PI = Microsoft Visual C++ compiler output Local float value of PI = Global double value of PI = Local float value of PI =

16 15.10 Function Overloading Function overloading: Functions with same name and different parameters Overloaded functions should perform similar tasks Function to square ints and function to square floats int square( int x) {return x * x;} float square(float x) { return x * x; } Program chooses function by signature Signature determined by function name and parameter types Type safe linkage - ensures proper overloaded function called C.E., NCU, Taiwan 16

17 1 // Fig : fig15_10.cpp 2 // Using overloaded functions 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 fig15_10.cpp 8 int square( int x ) { return x * x; } 9 10 double square( double y ) { return y * y; } int main() 13 { 14 cout << "The square of integer 7 is " << square( 7 ) 15 << "\nthe square of double 7.5 is " << square( 7.5 ) 16 << endl; return 0; 19 } // end function main The square of integer 7 is 49 The square of double 7.5 is